Small diameter nerve fibers (C fibers) play an important role in many physiological functions in the nervous system. These include the transmission of pain, temperature, and mechanoreceptor signals. In addition, C fibers are found in the autonomic nervous system and in many parts of the central nervous system as part of a diffuse network. Despite their abundance and importance, little is known about the physiology of C fibers because they are difficult to study. Their small (0.2 micron) diameter limits the use of micro-electrode or patch-clamp recording techniques nd their association with other fibers in mammalian nerves prevents their experimental isolation. The garfish olfactory nerve is a unique experimental model system in which to study the physiology of C fibers. This nerve was identified two decades ago as a homogenous source of uniform diameter C fibers, several inches in length. The objective of this pilot project is to study intracellular pH (pHi) regulation in vertebrate C fibers by using the garfish olfactory nerve as an experimental model system. Since nearly all cell activities, including excitability, are sensitive to changes in pHi, it is important to understand how these cells regulate pHi. The study will focus on recently described pHi regulating pathways: Na/H exchange and Na-dependent and Na-independent Cl/HCO3 exchanges. Many cells maintain tight control over pHi by regulating the relative activity of these pathways. The experimental approach of these pilot studies is to measure pH, by incorporating the fluorescent pH indicator, BCECF, into the axons. Specific pHi regulating pathways will be identified by the use of specific inhibitors and ion substitutions after challenging the nerve with acid or alkaline loads. These pilot studies will provide a basis for more extended research into other aspects of ion regulation and excitability in small nerve fibers. For example, the interaction between pHi and intracellular Ca (Cai) will be studied in C fibers with the Ca sensitive fluorescent probe, fura-2. General anesthetics, reported to affect both pHi and Cai in the squid giant axon, will be tested for their effects on pHi and Cai regulation in C fibers.